The present invention relates generally to a medical device for diagnosing tissue and methods of use, and more particularly, to a medical device and methods for identifying abnormal tissue over a range of tissue temperatures manipulated according to the Peltier effect for effective tissue diagnosis.
Cancer and tumor are abnormal tissue that exhibits tissue characteristics different from those of the normal tissue. Breast cancer is the leading cause of death in women. The outlook for a wonder drug or vaccine to mitigate or cure the disease at any stage is not promising. It is known that our present methods of surgery, radiotherapy, and chemotherapy are effective for long-term survival if applied when the disease is detected early and confined locally to the breast.
The latest imaging techniques may detect diminutive danger signs and help recognize disease indicators during their early stage when treatment may be most beneficial. One established technique is mammography, which is used for early detection of small, treatable breast cancers. But mammography is not infallible. According to one estimate, mammography misses 10 to 15% of all malignancies. In cases where the test results are inconclusive, patients must usually undergo biopsy procedures.
This disclosure relates to a medical device and methods of differentiating in a given area of tissue a tumorous tissue from a normal tissue by measuring tissue characteristics in situ across a range of tissue temperatures and comparing the measured tissue characteristics with reference adapted for tissue differentiation, wherein the tissue characteristics may comprise electric impedance signal, acoustic impedance signal and others.
It is known to measure the electrical impedance of tissue to determine aspects of tissue structure. A technique is available as xe2x80x9celectrical impedance tomographyxe2x80x9d in which a number of impedance readings are taken at spaced apart locations on a region of the human body and an image derived from the data. Further, Brown et al. in PCT WO 01/67098 discloses a method of differentiating tissue types using impedance measurements over a range of frequencies. It has been shown that the tissue impedance decreases at higher frequencies, probably due to current penetration at the cell membrane.
Sollish et al. in U.S. Pat. No. 4,458,694, the disclosures of which are incorporated herein by reference, discloses systems in which the impedance between a point on the surface of the skin and some reference point on the body of a patient is determined. The reference prior art describes the use of a multi-element probe for the detection of cancer, especially breast cancer, utilizing detected variations of impedance in the breast. However, the skin surface impedance measurement is not site-specific for breast cancer diagnosis.
Pearlman in U.S. Pat. Nos. 5,810,742, 6,055,452, 6,308,097 and xe2x80x9cNew Imaging Techniques Detect Diminutive Danger Signsxe2x80x9d by W. Leventon (MDandDI pp 48-57, October 2000), the disclosures of which are incorporated herein by reference, describe transspectral impedance scanning (T-scan) systems as a new mammography for cancer identification. The T-scan measures the movement of electricity through tissue because cancers have impedance values that are much lower than those of noncancerous tissue. It is further disclosed that the capacitance and conductance of malignant tissue are about 50 times greater than that of either normal tissue or benign lesions. However, the T-scan neither measures the site-specific minute tumor or cancer in vivo, nor manipulates the tested tissue at a range of temperatures suitable for enhancedly differentiating the impedance signal of the cancers from that of noncancerous tissue over a range of tissue temperatures.
The sonography uses high frequency sound waves to perform a wide variety of diagnostic examinations. The ultrasound frequencies typically range from about 20 kHz to above 100 MHz. The principles of diagnostic sonography rest in the tissue attenuation, reflectivity, transmission or scattering, which has been described elsewhere (C J Pavlin and F S Foster, Ultrasound Biomicroscopy of the Eye, Chapter 1, by Springer-Verlag 1995).
Adachi et al. in U.S. Pat. No. 6,298,726, the entire contents of which are incorporated herein by reference, discloses an acoustic impedance measuring apparatus that emits ultrasonic waves to a target object and measures the acoustic impedance of the target object by ultrasonic waves fed back. The reference fails to teach manipulating the target tissue object at a range of temperatures to enhancedly differentiate the acoustic impedance signal of the cancer tissue object from that of noncancerous tissue object.
It would overcome the afore-mentioned disadvantages by providing a needle probe and a method of differentiating in a given area of tissue a tumorous tissue from a normal tissue, the method comprising measuring tissue impedance, electrically, acoustically or thermally, across a range of tissue temperatures and comparing the measured tissue impedance with reference tissue impedance of the normal tissue adapted for enhanced tissue differentiation.
To maintain the tissue temperature over a range, say from 20xc2x0 C. to 45xc2x0 C., thermal energy and cryogenic cooling is provided alternatively. Conventionally thermal energy could be clinically applied to the tissue by radiofrequency heating, while the cryogenic cooling could be provided by a circulating cooled medium in the probe. A radiofrequency probe with a liquid-cooled electrode is conventionally used to manipulate the tissue temperature over a range of clinical interest. However, such a device is bulky and also cumbersome to handle the liquid cooling system. In one embodiment, the range of tissue temperatures of the present invention is about 20xc2x0 C. to 45xc2x0 C. that is suitable and compatible with the body tissue.
U.S. Pat. No. 5,348,554 to Imran et al. discloses a catheter system with a cooled electrode. Specifically, an electrode having a chamber therein is provided with a circulated cooling liquid to cool the electrode. U.S. Pat. No. 6,241,666 to Pomeranz et al., and U.S. Pat. No. 6,015,407 to Rieb et al. also disclose a catheter system with a modified cooled electrode, mostly with a liquid coolant arrangement that is bulky, expensive or poses unnecessary risk to a patient. The entire contents of the above-cited patents are incorporated herein by reference.
A radiofrequency catheter with a liquid-cooled electrode includes extra auxiliary equipments, such as a circulating pump, a cooling liquid source, control instruments, and accessories. As disclosed in U.S. Pat. No. 5,348,554, the cooled liquid is intended to cool the inner chamber of the tip electrode. However, the temperature of the outer surface of the electrode may rise to an unacceptable level resulting in tissue degradation, blood clot, or coagulation. As is well known to an ordinary technician skilled in the art that the resistive heat of radiofrequency ablation comes from the tissue-electrode contact surface. Even with a liquid-cooled setup thereof, the electrode temperature might be far above the cell necrosis temperature.
A probe for quantifying the impedance over a range of tissue temperature would be ideal for breast cancer diagnosis. Johnson et al. in U.S. Pat. No. 4,860,744 discloses a thermoelectrically controlled heat medical catheter, which is incorporated herein by reference. More particularly, Johnson et al. discloses a system and methods for providing controlled heating or cooling of a small region of body tissue to effectuate the removal of tumors and deposits, such as atheromatous plaque. Though Johnson et al. teaches a medical catheter in accordance with the Peltier effect adapted for thermoelectric heating/cooling for destruction of diseased tissue and/or tumors in various parts of the body, Johnson et al. does not disclose a method for manipulating the tissue temperatures so as to enhancedly differentiate the impedance signal of the cancers from that of noncancerous tissue over a range of tissue temperatures.
Larsen et al. in U.S. Pat. Nos. 5,529,067, 5,755,663, and 5,967,976 disclose methods and apparatus for use in procedures related to the electrophysiology of the heart, such as identifying or evaluating the electrical activity of the heart, diagnosing and/or treating conditions associated with the electrophysiology of the heart, entire contents of which are incorporated herein by reference. Specifically, Larsen et al. teaches an apparatus having thermocouple elements of different electromotive potential conductively connected at a junction and reducing the temperature of the junction in accordance with the Peltier effect for cooling the contacted heart tissue. However, Larsen et al. does not teach a method for diagnosing a target tissue comprising providing thermal or cryogenic energy to the target tissue and simultaneously or subsequently measuring tissue impedance over a range of tissue temperatures.
It is one object of the present invention to provide a method of differentiating a tumorous breast tissue from a normal tissue, wherein the method comprises measuring tissue characteristics across a range of tissue temperatures and comparing the measured tissue characteristics with reference characteristics of the normal tissue. There is a clinical need to screen the patients by a less invasive needle probe technique so as to lower the number of unnecessary biopsies performed each year.
In general, it is an object of the present invention to provide a device and a method for diagnosing and/or treating a target tissue using a medical device that is suitable for the intended applications in treating tumorous tissue, comprising a catheter, a probe, a cannula, an endoscopic instrument, a lapascopic instrument or the like.
It is another object of the present invention to provide a method of differentiating in a given area of tissue a tumorous tissue from a normal tissue, the method comprising measuring a plurality of tissue impedance over a range of tissue temperatures and comparing the measured tissue impedance with reference tissue impedance of the normal tissue adapted for tissue differentiation.
In one embodiment, the method of manipulating the tissue temperatures over the range of interest may be provided by a probe junction, the probe junction being conductively connected to two elements of different electromotive potential and electrical current being passed through the elements to reduce/raise temperature of the probe junction in accordance with the Peltier effect.
In another embodiment, the target tissue may be selected from a group consisting of tumor, cancerous tissue, arrhythmia, pulmonary vein, benign prostate hyperplasia, breast tumor, breast cancer, inflammation, atherosclerosis, vulnerable plaque, or the like. The therapeutic thermal energy may be selected from a group consisting of radiofrequency energy, microwave energy, laser energy, infrared energy, ultrasound energy, and combination thereof.
It is another object of the present invention to provide an electric impedance, acoustic impedance, or biochemical impedance over a range of tissue temperatures for tissue differentiation.
It is still another object of the present invention to provide a probe for treating tissue subsequent to identifying a tumorous tissue. The treatment methods may comprise thermal ablation, cryogenic ablation, delivering a therapeutic means for treating the tumorous tissue at about said given area of tissue, wherein the therapeutic means is selected from a group consisting of drug, chemotherapy, radiation, and combination thereof.